Abstract: A uniform-field resonator includes a central cavity section having a cross-section which is set to the cutoff frequency for a particular microwave propagation mode and a pair of end sections which enclose the cavity to form a resonator in which the field is substantially uniform along the entire length of the central cavity—regardless of its length. A number of end section design strategies and resulting structures are described for supporting the uniform-field mode of operation in the central cavity section.

Abstract: A uniform-field resonator includes a central cavity section having a cross-section which is set to the cutoff frequency for a particular microwave propagation mode and a pair of end sections which enclose the cavity to form a resonator in which the field is substantially uniform along the entire length of the central cavity—regardless of its length. A number of end section design strategies and resulting structures are described for supporting the uniform-field mode of operation in the central cavity section.

Abstract: Counter Rotating Current (CRC) pairs of loop-gap resonators are combined with planar pairs of loop-gap resonators to form networks of NMR local coils. A first embodiment is a quadrature probe in which a planar pair is sandwiched between the loop-gap resonators of the CRC pair. In a plurality of other embodiments, CRC pairs, planar pairs, and other types of local coils are arranged adjacent to one another to form networks of NMR local coils with an enlarged net region of sensitivity. In a further embodiment of the invention, an excitation coil operated in an excite/receive mode is combined with intrinsically isolated local detectors to form an NMR detection network.

Abstract: A local coil for use in NMR imaging includes a pair of loop-gap resonators which are geometrically arranged to be intrinsically isolated. The local coil also includes passive decoupling means to completely decouple the local coil during excitation. In a first embodiment, the pair of loop-gap resonators are disposed axially and the passive decoupling means comprises a pair of back-to-back diodes across the loop-gap resonators. In a second embodiment, the pair of loop-gap resonators are disposed in a plane and the passive decoupling means comprises two single turn loops inside each loop-gap resonator with back-to-back diodes across an open segment of each single turn loop. During excitation, the diodes fire thereby lowering the Q and shifting the resonant frequency of the local coil. Using a combination of intrinsic isolation and passive decoupling, the local coil is completely decoupled from the excitation field.

Abstract: A local probe for use in nuclear magnetic resonance imaging includes a pair of loop-gap resonators which are connected together and positioned adjacent a region of interest. FID signals produced in the region of interest induce signals in coupling loops mounted near each loop-gap resonator, and these connect to a transmission line leading to the receiver. Three embodiments are disclosed, one best suited for imaging appendages, a second best suited for imaging the head and neck, and a third best suited for the spine.

Abstract: Counter Rotating Current (CRC) pairs of loop-gap resonators are combined with planar pairs of loop-gap resonators to form networks of NMR local coils. A first embodiment is a quadrature probe in which a planar pair is sandwiched between the loop-gap resonators of the CRC pair. In a plurality of other embodiments, CRC pairs, planar pairs, and other types of local coils are arranged adjacent to one another to form networks of NMR local coils with an enlarged net region of sensitivity.

Abstract: The thickness of a web is measured by passing the web through the gaps of a loop-gap resonator. Changes in web thickness alter the resonant frequency of the resonator which is detected by a control circuit. Three embodiments of the invention are described, and in one embodiment, the moisture content of the web is also measured.

Abstract: An ESR spectrometer is employed to measure the oxygen concentration in a sample material. Electron paramagnetic resonance is produced in a free radical mixed with a standard material of known oxygen concentration. The phase of the signal produced by this resonance is compared with the phase of the signal produced by the electron paramagnetic resonance of the free radical mixed with the sample material. The oxygen concentration in the sample material has a single valued functional relationship with respect to this phase difference and is calculated in a microprocessor-based control system. At low oxygen concentrations, the relationship is a linear one.

Abstract: The ends of a loop-gap resonator are extended along a closed path to define an enclosed chamber with a gap extending along its length. A lumped circuit resonator is formed and the magnetic field is confined to the chamber. Openings may be formed in the chamber wall to direct magnetic flux through sample materials outside the chamber, and the cross sectional area of the chamber may be altered to control the energy density distribution of the magnetic field.

Abstract: A lumped circuit loop-gap resonator is formed by a plurality of openings formed through a block of material. The openings form inductive loop elements and these are interconnected in a variety of possible networks by capacitive gap elements. String, star, ring and lattice networks are described.

Abstract: A structure for supporting a loop-gap resonator includes a cylindrical housing which defines a space into which microwave energy is injected. The resonator is mounted to a support element which is inserted into the space through an opening at one end of the housing. The support element and attached resonator form an interchangeable module.

Abstract: A microwave resonator is formed by a cylindrical conductive loop and one or more gaps which extend along its length. The loop forms an inductive element and the gaps form capacitive elements which determine the resonant frequency. The loop is surrounded by a conductive shield which improves the quality factor (Q) of the resonator and high frequency radio signals are coupled to the resonator by an inductive loop positioned at one of its ends.

Abstract: A microwave resonator is formed by a cylindrical loop and one or more gaps which extend along its length. The loop is formed from a machineable insulating material and a layer of electrically conductive material is deposited over its surfaces.